They have not changed anything in forever. Even the boot loader is unlocked.

I install tons of software with homebrew and nix every day. Yes, sometimes you need to allow a new version explicitly. Also yes, Apple could probably disallow that globally, but that would be a big change for something they allowed for 50 years.

I think this will definitely come. It’s just a matter of time.

It runs macOS so you can install any stuff that you want. With asahi Linux showing you can also install other operating systems. I think a retrograde lockdown might be possible, but it’s unlikely.